When sawing crystalline rods of, for example, silicon, gallium arsenide, indium phosphide, sapphire or gallium-gadolinium garnet into wafers of approximately from 0.1 to 1 mm thickness, internal-hole saws are customarily used. An internal-hole saw comprises a rotating, circular saw blade that is clamped at its outside edge and has, in the centre, a hole having a diameter of a few centimeters, the circumference of the hole being set with diamonds and forming the actual cutting edge. When a crystalline rod is to be cut into wafers, it is first passed into the hole in the centre of the saw blade to a depth corresponding to the desired wafer thickness. Then, either the rod, which can be rotating, is moved outwards against the rotating cutting edge (see, for example, U.S. Pat. Nos. 3,025,738 and 3,039,235), or the rotating saw blade, is guided through the crystalline rod. In the final phase of cutting, uncontrolled breaks in weak residual portions between wafer and rod, breaks in the wafer and rod, breaks in the wafer surface, or breakage and loss of the whole wafer may occur due to the thinness of the wafer (usually approximately 400 um), the brittleness of the material, or the sucking action of the rotating saw blade.
Attempts have been made to solve the breakage problem by use of expensive removal devices (see, for example, DE-OS No. 30 10 867). In the method disclosed in the patent, the crystalline rod to be sawed is cemented to a cutting ledge which is not completely cut through during the sawing operation. The cutting ledge is useful for holding and feeding the rod and for stabilising the separated wafer. Apart from the expensive apparatus, the arrangement requires that each individual wafer be removed immediately after the cutting operation. The device therefore cannot be used with an internal-hole saw having a plurality of saw blades. Internal-hole saws with multiple blades are useful when an increase in cutting capacity is desired.